Electric power assist device and bicycle

ABSTRACT

An electric power assist device (50) includes a first to a third pedal force estimating computation unit (152, 154, 156) that estimate the pedal force of the bicycle according to variances between values of a first to a third state quantity detected by the first to third pedal force estimating computation units at two mutually different crank angle positions, a motor drive control unit (164) configured to control a drive of an electric motor according to a selected one of the pedal forces estimated by the first, the second and the third state quantity detecting units, and a failure diagnosis unit (158) configured to diagnose failures of the first, the second and the third state quantity detecting units by evaluating the variances in the values of first, the second and the third state quantities.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Phase Application ofPCT/JP2021/005847, filed on Feb. 17, 2021, which claims the benefit ofpriority to Japanese Patent Application No. 2020-056873, filed Mar. 26,2020. The contents of these applications are hereby expresslyincorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to an electric power assist device and abicycle, and particularly to a control arrangement for an electric motorthat provides an assist force.

BACKGROUND ART

In regard to electrically assisted bicycles, it is known to measure thestrain in the pedal system by using a strain gauge, and control theoperation of the electric motor according to the pedal force computedfrom the measured strain in the pedal system (see Patent Document 1, forexample), and it is also known to control the operation of the electricmotor according to the pedal force which is detected by a pedal forcesensor including a pedal force transmission sleeve attached to acrankshaft configured to be driven by the pedal (see Patent Document 2,for example).

PRIOR ART DOCUMENT(S) Patent Document(s)

-   Patent Document 1: JP2007-91159A-   Patent Document 2: U.S. Pat. No. 6,196,347B1

In these conventional electrically power assisted bicycle, a straingauge or a pedal force sensor is required to be attached to the pedal,the crankshaft, or the like in order to detect the pedal force with theresult that the structure tends to be complex. In particular, if thepedal force is to be detected by using a strain gauge or a pedal forcesensor in an existing bicycle, a substantial modification of the bicycleis required.

The applicant of the present application has previously proposed atechnology whereby the pedal force is estimated from the fore and aftacceleration of the bicycle detected by an acceleration sensor, from theangular velocity of a rotating member equivalent to the crankshaftdetected by a rotational angle sensor, and from the current of theelectric motor detected by a current sensor, and the assist force by theelectric motor is controlled according to the estimated pedal forcewithout using a strain gauge or a pedal force sensor.

In estimating the pedal force in this manner, if the accelerationsensor, rotational angle sensor, or current sensor should fail, theestimation of the pedal force cannot be performed correctly so that theassist operation is required to be disabled. In the electricallyassisted bicycle, once the assist operation is disabled, the rider isrequired to rotationally drive the electric motor by pedaling so that asubstantial pedaling effort will be required. For this reason, when afailure occurs in an electrically power assisted bicycle, the physicalburden on the rider significantly increases.

In view of such a problem of the prior art, a primary object of thepresent invention is to individually detect a failure among a pluralityof sensors used for estimating the pedal force, and reduce thepossibility of losing the assist function due to a sensor failure.

Means to Accomplish the Task

To achieve such an object, a certain aspect of the present inventionprovides an electric power assist device (50) configured to be fitted toa bicycle (10), comprising; an electric motor (58) connected to acrankshaft (24) configured to be driven by a pedal force applied to apedal of the bicycle via a crank arm (26) or to the crank arm in atorque transmission relationship; a first, a second and a third statequantity detecting unit (130, 134, 136) configured to individuallydetect a first, a second and a third state quantity which are mutuallydistinct for estimating the pedal force of the bicycle; and a controlunit (150) configured to control an operation of the electric motorbased on outputs of the first, the second and the third state quantitydetecting units, wherein the control unit includes: a first pedal forceestimating computation unit (152) configured to estimate the pedal forceof the bicycle according to a variance between values of the first statequantity at two mutually different crank angle positions; a second pedalforce estimating computation unit (154) configured to estimate the pedalforce of the bicycle according to a variance between values of thesecond state quantity at two mutually different crank angle positions; athird pedal force estimating computation unit (156) configured toestimate the pedal force of the bicycle according to a variance betweenvalues of the third state quantity at two mutually different crank anglepositions; a motor drive control unit (164) configured to control adrive of the electric motor according to a selected one of the pedalforces estimated by the first, the second and the third state quantitydetecting units; and a failure diagnosis unit (158) configured todiagnose failures of the first, the second and the third state quantitydetecting units by evaluating the variances in the values of first, thesecond and the third state quantities.

Thereby, failures of a plurality of sensors used for estimating thepedal force can be detected individually.

In this electric power assist device, preferably, the motor drivecontrol unit is configured to control the drive of the electric motoraccording to the pedal force estimated by one of the first pedal forceestimating computation unit, the second pedal force estimatingcomputation unit, and the third pedal force estimating computation unitcorresponding to one of the first to the third state quantity detectingunits that is diagnosed to be not faulty by the failure diagnosis unit.

Thereby, the possibility of stopping the power assist operation due tothe failure of the first to third state quantity detecting units can beminimized.

In this electric power assist device, preferably, one of the twomutually different crank angle positions includes a top dead center ofthe pedal, and another of the two mutually different crank anglepositions includes a crank angle position 90 degrees sway from the topdead center of the pedal.

Thereby, the variances between the values of the first to third statequantities at the two different crank angle positions can be made highlydistinct so that failure detection and pedal force estimation can beperformed with high accuracy.

In this electric power assist device, preferably, the first pedal forceestimation calculation unit is configured to estimate the pedal forceaccording to a variance between average values of the first statequantity averaged over two rotational angle ranges containing the twomutually different crank angle positions, respectively, the second pedalforce estimation calculation unit is configured to estimate the pedalforce according to a variance between average values of the second statequantity averaged over two rotational angle ranges containing the twomutually different crank angle positions, respectively, and the thirdpedal force estimation calculation unit is configured to estimate thepedal force according to a variance between average values of the thirdstate quantity averaged over two rotational angle ranges containing thetwo mutually different crank angle positions, respectively.

Thereby, the accuracy of failure detection and pedal force estimationcan be improved.

In this electric power assist device, preferably, the first to thirdstate quantity detecting units are selected from an acceleration sensor(134) for detecting a fore and aft acceleration of the bicycle, arotational angle sensor (130) for detecting a crank angle and a crankangular velocity of the crankshaft, and a current sensor (136) fordetecting a motor current value of the electric motor.

Thereby, failures of the acceleration sensor, the rotational anglesensor, and the current sensor can be individually determined.

In this electric power assist device, preferably, the failure diagnosisunit is configured to determine the failures of the first to third statequantity detecting units by comparing the variances between the valuesof the first to third state quantities with corresponding first to thirdthreshold values, respectively.

Thereby, the failures of the first to third state quantity detectingunits can be individually determined.

In this electric power assist device, preferably, the failure diagnosisunit is configured to diagnose the first state quantity detecting unitto be normal when the variance in regard to the first state quantity isin a prescribed magnitude relationship to the first threshold value, andthe first state quantity detecting unit to be faulty when the variancein regard to the first state quantity is not in the prescribed magnituderelationship to the first threshold value; the failure diagnosis unit isconfigured to diagnose the second state quantity detecting unit to benormal when the variance in regard to the second state quantity is in aprescribed magnitude relationship to the second threshold value, and thesecond state quantity detecting unit to be faulty when the variance inregard to the second state quantity is not in the prescribed magnituderelationship to the second threshold value; and the failure diagnosisunit is configured to diagnose the third state quantity detecting unitto be normal when the variance in regard to the third state quantity isin a prescribed magnitude relationship to the third threshold value, andthe third state quantity detecting unit to be faulty when the variancein regard to the third state quantity is not in the prescribed magnituderelationship to the third threshold value.

Thereby, the failure determination of the first to third state quantitydetecting units can be performed in a sequential manner so that failuredetection of the first to third state quantity detecting units can beprioritized.

In this electric power assist device, preferably, the motor drivecontrol unit is configured to control the drive of the electric motoraccording to the pedal force estimated by the first pedal forceestimating computation unit when the first pedal force estimatingcomputation unit is determined to be normal by the failure diagnosisunit; to control the drive of the electric motor according to the pedalforce estimated by the second pedal force estimating computation unitinstead of the first pedal force estimating computation unit when thefirst pedal force estimating computation unit is determined to be faultyby the failure diagnosis unit; to control the drive of the electricmotor according to the pedal force estimated by the third pedal forceestimating computation unit instead of the second pedal force estimatingcomputation unit when the second pedal force estimating computation unitis determined to be faulty by the failure diagnosis unit; and toterminate the drive of the electric motor when the third pedal forceestimating computation unit is determined to be faulty by the failurediagnosis unit.

Thereby, the possibility of stopping the assist operation due to thefailures of the first to third state quantity detecting units can bereduced.

In this electric power assist device, preferably, the failure diagnosisunit is configured to determine the failures of the first to third statequantity detecting units by comparing the variances in regards to thefirst to third state quantities with one another.

Thereby, the accuracy of failure detection of the first to third statequantity detecting units can be improved.

In this electric power assist device, preferably, the first statequantity detecting unit includes an acceleration sensor for measuring afore and aft acceleration of the bicycle, the second state quantitydetecting unit includes a rotational angle sensor for detecting a crankangle and a crank angular velocity of the crankshaft, and the thirdstate quantity detecting unit includes a current sensor for detecting amotor current value of the electric motor.

Thereby, failures of the acceleration sensor, the rotational anglesensor, and the current sensor can be individually determined.

In this electric power assist device, preferably, the failure diagnosisunit is configured to diagnose all of the acceleration sensor, therotational angle sensor, and the current sensor to be normal in casewhere the variance in the vehicle body acceleration between the twomutually different crankshaft angles is equal to or greater than afourth threshold value when the variance in the crankshaft angularvelocity between the two mutually different crankshaft angles is equalto or greater than a fifth threshold value, if the variance in the crankangular velocity between the two mutually different crankshaft angles isequal to or greater than a fifth threshold value when the variance inthe motor current between the two mutually different crankshaft anglesis equal to or greater than a sixth threshold value; to diagnose thatthe acceleration sensor to be faulty in case where the variance in thevehicle body acceleration between the two mutually different crankshaftangles is smaller than the fourth threshold value when the variance inthe crankshaft angular velocity between the two mutually differentcrankshaft angles is equal to or greater than the fifth threshold valueif the variance in the vehicle body acceleration between the twomutually different crankshaft angles is equal to or greater than thefourth threshold value when the variance in the motor current betweenthe two mutually different crankshaft angles is smaller than the sixththreshold value; to diagnose that the rotational angle sensor to befaulty in case where the variance in the vehicle body accelerationbetween the two mutually different crankshaft angles is smaller than thefourth threshold value when the variance in the crankshaft angularvelocity between the two mutually different crankshaft angles is equalto or greater than the fifth threshold value if the variance in thevehicle body acceleration between the two mutually different crankshaftangles is smaller than the fourth threshold value when the variance inthe motor current between the two mutually different crankshaft anglesis equal to or greater than the sixth threshold value; and to diagnosethat the motor current sensor to be faulty in case where the variance inthe vehicle body acceleration between the two mutually differentcrankshaft angles is equal to or greater than the fourth threshold valuewhen the variance in the crankshaft angular velocity between the twomutually different crankshaft angles is equal to or greater than thefifth threshold value if the variance in the crankshaft angular velocitybetween the two mutually different crankshaft angles is smaller than thefifth threshold value when the variance in the motor current between thetwo mutually different crankshaft angles is equal to or greater than thesixth threshold value.

Thereby, failures of the acceleration sensor, the rotational anglesensor, and the current sensor can be individually and accuratelydetermined.

In this electric power assist device, preferably, the failure diagnosisunit diagnoses that the current sensor is also faulty in case where theacceleration sensor is diagnosed to be faulty, and the variance in thecrank angular velocity is equal to or greater than the fifth thresholdvalue when the variance in the motor current value is equal to orgreater than the sixth threshold value if the variance in the motorcurrent value is smaller than the sixth threshold value when thevariance in the crank angular velocity is equal to or greater than thefifth threshold value; that the rotational angle sensor is also faultyif the acceleration sensor is diagnosed to be faulty, and the variancein the crank angular velocity is smaller than the fifth threshold valuewhen the variance in the motor current value is equal to or greater thanthe sixth threshold value; that the current sensor is also faulty incase where the rotational angle sensor is diagnosed to be faulty, andthe variance in the vehicle body acceleration is equal to or greaterthan the fourth threshold value when the variance in the motor currentvalues is equal to or greater than the sixth threshold value if thevariance of the motor current value is smaller than the sixth thresholdvalue when the variance in the vehicle body acceleration is equal to orgreater than the fourth threshold value; that the acceleration sensor isfaulty if the rotational angle sensor is diagnosed to be faulty, and thevariance in the vehicle body acceleration is smaller than the fourththreshold value when the variance in the motor current value is equal toor greater than the sixth threshold value; that the rotational anglesensor is also faulty in case where the current sensor is diagnosed tobe faulty, and the vehicle body acceleration is equal to or greater thanthe fourth threshold value when the variance in the crank angularvelocity is equal to or greater than the fifth threshold value if thecrank angular velocity is smaller than the fifth threshold value whenthe variance in the vehicle body acceleration is equal to or greaterthan the fourth threshold value; and that the acceleration sensor isalso faulty if the current sensor is diagnosed to be faulty, and thevehicle body acceleration is smaller than the fourth threshold valuewhen the crank angular velocity is equal to or greater than the fifththreshold value.

Thereby, failures of the acceleration sensor, the rotational anglesensor, and the current sensor can be individually and accuratelydetermined.

A bicycle according to one embodiment of the present invention is fittedwith the electric power assist device according to the above-describedembodiments.

Effect of the Invention

The present invention thus provides an electric power assist device thatindividually detects a failure among a plurality of sensors used forestimating the pedal force, and reduces the possibility of losing theassist function due to a sensor failure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary side view of a bicycle fitted with an electricpower assist device according to an embodiment of the present invention;

FIG. 2 is a fragmentary perspective view of the bicycle of the presentembodiment;

FIG. 3 is an exploded perspective of the electric power assist device ofthe present embodiment;

FIG. 4 is a block diagram of the control system of the electric powerassist device of the present embodiment;

FIG. 5 is a diagram illustrating the relationship between the pedalposition and the crank angular position in the electric power assistdevice of the present embodiment;

FIG. 6 is a graph showing the relationship between the fore and aftacceleration and the crank angular position of the bicycle;

FIG. 7 is a graph showing the relationship between the crank angularvelocity and the crank angular position of the bicycle;

FIG. 8 is a graph showing the relationship between the motor current andthe crank angular position of the bicycle;

FIG. 9 is a flowchart of an assist control in the electric power assistdevice of the present embodiment;

FIG. 10 is a flowchart of an assist control in the electric power assistdevice according to another embodiment of the present invention;

FIG. 11 is a flowchart of a normal control process;

FIG. 12 is a flowchart of a process at the time of a current sensorfailure;

FIG. 13 is a flowchart of a process at the time of a rotational anglesensor failure; and

FIG. 14 is a flowchart of a process at the time of an accelerationsensor failure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

A bicycle fitted with an electric power assist device according to anembodiment of the present invention will be described in the followingwith reference to the appended drawings.

As shown in FIGS. 1 to 3 , the bicycle 10 is provided with a framestructure 18 including a seat tube 12 extending substantially verticallyand having a saddle (not shown in the drawings) attached to the upperend thereof, a down tube 14 extending substantially in the fore and aftdirection, and a pair of chain stays 16 located on either side. Thelower end of the seat tube 12, the rear end of the down tube 14, and thefront ends of the chain stays 16 are commonly connected to one anotherby a bearing tube 20 for supporting a crankshaft also serving as a pipejoint.

The bearing tube 20 rotatably supports the crankshaft 24 extendingsubstantially horizontally in the lateral direction. The left and rightshaft ends of the crankshaft 24 project outward from the bearing tube20, and the base ends of the left and right crank arms 26 and 28 arefixed to the respective shaft ends with a rotational phase difference of180 degrees. The crankshaft 24 forms the rotational center of the crankarms 26 and 28, and the rotational center line of the crankshaft 24 andthe rotational center line of the crank arms 26 and 28 are on the sameaxial line.

Each shaft end of the crankshaft 24 is provided with a spline shaftportion 24A on the outer peripheral surface thereof. The base end ofeach crank arm 26 is formed with a spline hole 26A. The spline shaftportion 24A and the spline hole 26A are engaged with each other so thatthe crankshaft 24 and the crank arm 26 are connected in a torquetransmitting relationship.

The end surface of the crankshaft 24 is formed with a screw hole 24B(see FIG. 3 ) opening at the shaft end surface. The base end of thecrank arm 26 is formed with a screw hole 26B having an inner diameterlarger than that of the spline hole 26A and communicating coaxially withthe spline hole 26A. A crank arm mounting screw 27 is threaded into thescrew hole 24B, and is provided with a flange portion abutting on theannular shoulder surface defined between the spline hole 26A. As aresult, the crank arm 26 is prevented from coming off from thecrankshaft 24.

The connection between the crankshaft 24 and the other crank arm 28 isperformed in the same manner as the connection between the crankshaft 24and the crank arm 26 described above.

A pedal 30 is attached to the free end of each crank arm 26, 28. A drivesprocket (chain wheel) 32 is positioned between the crank arm 28 on theright side and the bearing tube 20. The drive sprocket 32 is coaxiallyconnected (fixed) to the crankshaft 24.

The crankshaft 24 is rotationally driven by the left and right crankarms 26 and 28. The rotation of the crankshaft 24 is transmitted to thedrive sprocket 32, and is transmitted from the drive sprocket 32 to therear wheel (not shown in the drawings) by a chain type transmissionmechanism (not shown in the drawings). Thereby, the bicycle 10 travelsforward.

The bicycle 10 has a modular electric power assist device 50 that can beretrofitted. In the following description, the vertical, fore and aftand lateral directions are defined with respect to the state where theelectric power assist device 50 is attached to the frame structure 18 ofthe bicycle 10 as shown in FIGS. 1 and 2 .

The electric power assist device 50 is provided with a housing 52 havinga hollow structure. The housing 52 includes a ring portion 54 and atongue shaped extension portion 56 extending radially outward from thering portion 54. An electric motor 58 is attached to the right side ofthe extension portion 56. One end of the electric motor 58 is fixed tothe extension portion 56 so that the rotational center line of theoutput shaft (not shown in the drawings) thereof extends in the lateraldirection.

As shown in FIG. 3 , the ring portion 54 includes a cylindrical portion62 that defines a central opening 60 that is open in the lateraldirection. The cylindrical portion 62 rotatably supports an annularrotary output member 64 on the outer peripheral part thereof. Thecylindrical portion 62 is positioned in the space defined between theframe structure 18 and the crank arm 26, along with the rotary outputmember 64, with the crankshaft 24 loosely passed through the centralopening 60 in the lateral direction. The rotary output member 64 isconnected to the electric motor 58 in a torque transmitting relationshipvia a gear train (not shown in the drawings) provided in the housing 52,and is rotationally driven by the electric motor 58 coaxially withrespect to the crankshaft 24.

The cylindrical portion 62 and the rotary output member 64 can beinstalled in the space defined between the frame structure 18 and thecrank arm 26 as will be described in the following.

First of all, the left pedal 30 located on the side where the drivesprocket 32 is not located is removed by using an ordinary tool such asa spanner. Then, with the electric power assist device 50 laid flat onone side (such that the electric motor 58 faces upward), the free end ofthe left crank arm 26 is passed into the central opening 60, and withthe crank arm 26 passed into the central opening 60, the electric powerassist device 50 is moved to the base end side (rotational center side)of the crank arm 26 along the length of the crank arm 26.

As a result, the cylindrical portion 62 and the rotary output member 64are moved along the crank arm 26 until the base end part of the crankarm 26 is reached. The inner diameter of the central opening 60 isselected so that this operation is possible. If the central opening 60has an inner diameter large enough to allow the pedal 30 to be passedtherethrough as well, the pedal 30 is not required to be removed forthis operation.

Next, the attitude of the electric power assist device 50 is changedsuch that the electric motor 58 faces sideways or is at its properorientation (the attitude shown in FIG. 1 ), and the crankshaft 24 isloosely passed through the central opening 60 in the axial direction. Asa result, the cylindrical portion 62 and the rotary output member 64 arepositioned between the frame structure 18 and the crank arm 26 with thecrankshaft 24 passed laterally and loosely through the central opening60 simply by removing the pedal 30 or without requiring to remove thepedal 30.

The rotary output member 64 is connected to the crankshaft 24 and thecrank arm 26 by a coupling mechanism 70 which includes a substantiallydisk-shaped coupling main member 72 and a pair of clamp members 74.

The screw hole 26B of the crank arm 26 threadably receives a male threadportion of a screw member 78 serving as a mount portion for mounting thecoupling main member 72 to the crank arm 26. The coupling main member 72is substantially circular dish shaped, and fixed to the rotary outputmember 64 at the peripheral part thereof by a plurality of bolts 75 andto the screw member 78 at the central part thereof by a bolt 76. As aresult, the rotary output member 64 is coaxially positioned on thecrankshaft 24 via the coupling main member 72 and the crank arm 26.

A pair of clamp members 74, each having a wedge shape, are positioned oneither side of a base end part of the crank arm 26 with respect to therotational direction so as to slidably engage inclined edge parts 73 ofthe coupling main member 72, respectively. The clamp members 74 arecaused to move toward each other as the clamp members 74 are fastened tothe coupling main member 72 by bolts 80, respectively, so that the clampmembers 74 clamp the crank arm 26 from both sides, and the coupling mainmember 72 and the crank arm 26 are connected to each other in a torquetransmitting relationship.

As a result, the rotary output member 64 is coaxially coupled to thecrankshaft 24 via the coupling main member 72 and the crank arm 26 in atorque transmitting relationship, and rotates integrally with thecrankshaft 24 together with the coupling main member 72. The rotaryoutput member 64 and the coupling main member 72 are collectivelyreferred to as a rotary member.

The through holes 81 (see FIG. 2 ) provided in the clamp members 74 forthe bolts 80 are each formed in an oval shape (track shape) so that thetwo clamp members 74 may move toward each other when the bolts 80 aretightened with respect to the coupling main member 72.

The extension portion 56 of the housing 52 is positioned below the downtube 14 with the electric motor 58 supported thereby, and is supportedby the frame structure 18 by being suspended from the down tube 14 by asupport mechanism 90.

The support mechanism 90 includes a mounting member 92 which is fixed tothe down tube 14 by a fastening band 94. The mounting member 92 includesa support base member 98 provided with a rectangular frame portion 96 ina lower part thereof, and a support member 104 including a rectangularplate portion 100 fixed to the support base member 98 by being fittedinto the rectangular frame portion 96, and a depending piece 102depending downward from the rectangular plate portion 100 and extendingin the fore and aft direction.

The depending piece 102 is a cantilever piece, and includes a throughhole 103 that is provided with a shoulder, and extends in the axialdirection (the lateral direction) of the crankshaft 24. A cylindricalfixed bush 106 is fitted in the through hole 103 of the depending piece102 so as to be restricted from moving rightward and rotationally fast(fixed).

A female screw 108 is formed on the inner peripheral surface of thefixed bush 106. A male screw 109 formed on the outer peripheral surfaceof a movable bush 110 is threaded into the female screw 108 so as to bethreaded into and out of the female screw 108 in the axial direction ofthe crankshaft 24 or in the lateral direction.

The movable bush 110 is provided with a flange portion 112 on the sidethereof facing away from the fixed bush 106. The outer circumference ofthe flange portion 112 is provided with an uneven shape like flowerpetals so that the movable bush 110 can be turned by hand. The flangesurface of the flange portion 112 directly opposes and is in directcontact with the end surface of a boss portion (joining portion) 66formed in an upper part of the extension portion 56 of the housing 52.

The mounting member 92 supports the housing 52 in a fixed condition bymeans of a fastening bolt 114 that is passed centrally through the fixedbush 106 and the movable bush 110 in the axial direction of thecrankshaft 24, and is threaded into a screw hole (not shown in thedrawings) of the boss portion 66.

In this manner, the female screw 108 of the fixed bush 106 and the malescrew 109 of the movable bush 110 jointly form a screw mechanism betweenthe housing 52 and the frame structure 18, and this screw mechanismserves as an adjustment mechanism for adjusting (increasing anddecreasing) the distance between the mounting member 92 and the housing52 in the axial direction of the crankshaft 24.

By adjusting this distance in the axial direction, the inclination ofthe rotary output member 64 with respect to the central axis (crankaxis) of the crankshaft 24 can be corrected. As a result, the attitudeof the rotary output member 64 can be corrected such that the rotaryoutput member 64 is in parallel with a plane orthogonal to the crankaxis.

A control unit 150 for electric power assist is incorporated in theextension portion 56 of the housing 52. A battery 120 consisting of asecondary battery for powering the electric motor 58 and the controlunit 150 is attached to the seat tube 12 by a fastening band (not shownin the drawings) or the like.

Next, the control system of the electric power assist device 50 will bedescribed in the following with reference to FIG. 4 .

The control unit 150 is connected to a rotational angle sensor 130, apulse sensor 132, an acceleration sensor 134, a current sensor 136, aninclination angle sensor 138, and a voltage sensor 140.

The rotational angle sensor 130 is provided in the electric motor 58 orthe housing 52 to detect the rotational angle of the motor or therotational angle of the rotary output member 64 as a rotational angle(hereinafter, crank angle) θc of the crankshaft 24. The control unit 150calculates the crank angular velocity ω, which is a first state quantitythat is related to the pedal force, by time integration of the crankangle θc detected by the rotational angle sensor 130. Thus, therotational angle sensor 130 forms a part of a second state quantitydetecting unit.

The pulse sensor 132 is provided in the housing 52 to detect a zeropoint (θc=0 degrees) of the crank angle θc for each rotation of therotary output member 64. As shown in FIG. 5 , the crank angle θc=0degrees is predefined to be the rotational angle of the crankshaft 24when the pedal 30 of the crank arm 26 is located at the highest position(top dead center position).

The actual zero point (θs=0 degrees) of the pulse sensor 132 may not bethe crank angle at which the pedal 30 is located at the highestposition, and may be, for example, a rotational angle corresponding tothe crank angle θc=300 degrees. In this case, the calibration operationfor eliminating the phase difference of 300 degrees between θc=0 degreesand θs=0 degrees is performed in the control unit 150.

The acceleration sensor 134 is a first state quantity detecting unit,which is provided in the housing 52 to detect the acceleration (vehiclebody acceleration) a in the fore and aft direction (traveling direction)of the bicycle 10 as a first state quantity that is related to the pedalforce.

As shown in FIG. 6 , the vehicle body acceleration α changes in responseto the

crank angle θc in a sinusoidal manner with a cycle of 180 degrees so asto be at the minimum at θc=0 degrees, at the maximum at θc=90 degrees,at the minimum once again at θc=180 degrees, at the maximum once againat θc=270 degrees, and at the maximum at θc=360 degrees, and is relatedto the peal force.

The control unit 150 calculates the crank angular velocity ω, which is asecond state quantity that is related to the pedal force, by timeintegration of the crank angle θc detected by the rotational anglesensor 130. Thus, the rotational angle sensor 130 forms a part of asecond state quantity detecting unit.

As shown in FIG. 7 , the crank angular velocity ω is at a minimum atθc=0 degrees and increases from at about θc=60 degrees in a cycle of 180degrees, and is related to the pedal force.

The current sensor 136 is a third state quantity detecting unit, anddetects the motor current value i of the electric motor 58 as a thirdstate quantity that is related to the pedal force.

As shown in FIG. 8 , the motor current value i is at a maximum at θc=0degrees, and decreases from at about θc=60 degrees in a cycle of 180degrees, and is related to the pedal effort.

The inclination angle sensor 138 is provided on the housing 52 to detectthe tilt angle of the frame structure 18 of the bicycle 10 with respectto the direction of gravity, or the tilt angle of the frame structure 18of the bicycle 10 in the fore and aft direction and the lateraldirection with respect to the plumb line.

Both the vehicle body acceleration a detected by the acceleration sensor134 and the inclination angle of the bicycle 10 with respect to theplumb line detected by the inclination angle sensor 138 may also beacquired by arithmetically processing the output signal of a gyro sensorprovided with a G sensor.

The voltage sensor 140 detects the voltage of the battery 120.

The control unit 150 is an electronically controlled device including amicrocomputer and the like, and is provided with a first pedal forceestimation calculation unit 152, a second pedal force estimationcalculation unit 154, a third pedal force estimation calculation unit156, a failure diagnosis unit 158, a crank rotational directiondetermination unit 160, a pedal force detection unit 162, and a motordrive control unit 164.

The first pedal force estimation calculation unit 152 may also be calledas a pedal force estimation calculation unit corresponding to thevehicle body acceleration. The first pedal force estimation calculationunit 152 receives information on the crank rotational angle θc from therotational angle sensor 130, information on the crank rotational angleθc=0 degrees of the crankshaft 24 from the pulse sensor 132, andinformation on the vehicle body acceleration α from the accelerationsensor 134 with respect to the fore and aft direction of the bicycle 10,and estimates the pedal force of the bicycle 10 from the variancebetween the average value A1 of the vehicle body acceleration a over acrank angle range θ1 as measured from the angular position θc=0 degrees,for instance over the angle range of 01=0 to 60 degrees, and the averagevalue A2 of the vehicle body acceleration α over a crank angle range θ2as measured from the angular position θc=0 degrees, for instance overthe angle range of θ1=60 to 120 degrees, in the normal rotationaldirection.

The variance between the average value A1 and the average value A2 ofthe vehicle body acceleration α may be either an arithmetic difference(A2-A1) or a ratio (A2/A1) between the two values. The first pedal forceestimation calculation unit 152 estimates that the pedal force isgreater with an increase in the difference (A2−A1) or the ratio (A2/A1)between the two values

The pedal force is estimated from the variance between the average valueA1 of the vehicle body acceleration α over a crank angle range θ1including the crank angle θc=0 degrees at which the vehicle bodyacceleration α due to pedaling is at a minimum, and the average value A2of the vehicle body acceleration α over a crank angle range θ2 includingθc=90 degrees at which the vehicle body acceleration α due to pedalingis at a minimum. Therefore, the pedal force can be estimated at a highprecision as compared with the case where the vehicle body accelerationα at the crank angle θc=0 degrees and θc=90 degrees is not included orthe average values are not used.

When information on the crank angle θc cannot be obtained from therotational angle sensor 130 due to a failure in the rotational anglesensor 130, the first pedal force estimation calculation unit 152estimates the pedal force of the bicycle 10 from the absolute value ofthe vehicle body acceleration α during a revolution of the crankshaft 24which can be obtained from the signal from the pulse sensor 132.

The second pedal force estimation calculation unit 154 may be consideredas a pedal force estimation calculation unit based on the crank angularvelocity. The second pedal force estimation calculation unit 154receives information on the crank rotational angle θc from therotational angle sensor 130, information on the crank rotational anglebeing 0 degrees (θc=0 degrees) from the pulse sensor 132, andinformation on the crank angular velocity ω which is to be integrated toprovide the crank angle θc from the rotational angle sensor 130. Thepedal force is estimated from the variance between the average value Ω1of the crank angular velocity ω over a prescribed crank angle range θ2as measured from θc=0 degrees, for instance over a crank angle rangeθc=0 degrees to 60 degrees (angle range θ2) in the normal rotationaldirection, and the average value Ω2 of the crank angular velocity ω overa prescribed crank angle range θ2 as measured from θc=0 degrees, forinstance over a crank angle range θc=60 degrees to 120 degrees (anglerange θ2) in the normal rotational direction.

The variance between the average value Ω1 and the average value Ω2 ofthe crank angular velocity ω is either a difference (Ω2−Ω1) or a ratio(Ω2/Ω1) between the two values. The second pedal force estimationcalculation unit 154 estimates that the pedal force is greater with anincreased in the difference (Ω2−Ω1) or the ratio (Ω2/Ω1) between the twovalues.

The pedal force is estimated from the variance between the average valueΩ1 of the crank angular velocity ω over a prescribed crank angle rangeθ1 that contains θc=0 degrees where the crank angular velocity ω due topedaling is at a minimum and the average value Ω2 of the crank angularvelocity ω over a prescribed crank angle range θ2 that contains θc=90degrees where the crank angular velocity ω due to pedaling is at amaximum. Therefore, the pedal force can be estimated at a high precisionas compared with the case where the crank angular velocity ω at thecrank angle θc=0 degrees and θc=90 degrees is not included or theaverage values are not used.

When information on the crank angle θc cannot be obtained from therotational angle sensor 130 due to a failure in the rotational anglesensor 130, the second pedal force estimation calculation unit 154estimates the pedal force of the bicycle 10 from the absolute value ofthe crank angular velocity ω during a rotation of the crankshaft 24which can be obtained from the signal from the pulse sensor 132.

The third pedal force estimation calculation unit 156 may be consideredas a pedal force estimation calculation unit based on the motor currentvalue. The third pedal force estimation calculation unit 156 receivesinformation on the crank angle θc from the rotational angle sensor 130,information on the rotational angle θc=0 degrees of the crankshaft 24from the pulse sensor 132, and information on the motor current value ifrom the current sensor 136. The pedal force is estimated from thevariance between the average value I1 of the motor current value i overa prescribed crank angle range θ2 as measured from θc=0 degrees, forinstance over a crank angle range θc=0 degrees to 60 degrees (anglerange θ2) in the normal rotational direction, and the average value I2of the motor current value i over a prescribed crank angle range θ2 asmeasured from θc=0 degrees, for instance over a crank angle range θc=60degrees to 120 degrees (angle range θ2) in the normal rotationaldirection.

The variance between the average value I1 and the average value I2 ofthe crank angular velocity ω is either a difference (I2−I1) or a ratio(I2/I1) between the two values. The third pedal force estimationcalculation unit 156 estimates that the pedal force is greater with anincreased in the difference (I2−I1) or the ratio (I2/I1) between the twovalues.

The pedal force is estimated from the variance between the average valueI1 of the motor current value i over a prescribed crank angle range θ1that contains θc=0 degrees where the motor current value i due topedaling is at a minimum and the average value I2 of the motor currentvalue i over a prescribed crank angle range θ2 that contains θc=90degrees where the motor current value i due to pedaling is at a maximum.Therefore, the pedal force can be estimated at a high precision ascompared with the case where the motor current i at the crank angle θc=0degrees and θc=90 degrees is not included or the average values are notused.

When information on the crank angle θc cannot be obtained from therotational angle sensor 130 due to a failure in the rotational anglesensor 130, the third pedal force estimation calculation unit 156estimates the pedal force of the bicycle 10 from the absolute value ofthe motor current value i during a rotation of the crankshaft 24 whichcan be obtained from the signal from the pulse sensor 132.

The failure diagnosis unit 158 diagnoses the rotational angle sensor130, the acceleration sensor 134, and the current sensor 136 forfailures by evaluating the variances of the vehicle body acceleration α,the crank angular velocity ω, and the motor current value i, which arethe first to third state quantities. When any of the sensors 130, 134,and 136 is determined to be faulty by performing failure diagnosis oneach of the sensors 130, 134, and 136, the failure display unit 166 isturned active (turned on) by turning on a warning lamp or the like.

In a particular embodiment of the present invention, the failurediagnosis unit 158 determines that the acceleration sensor 134 is normalif the variance in the vehicle body acceleration α has a predeterminedmagnitude relationship with respect to a first threshold value, anddetermines that the acceleration sensor 134 is faulty if the variance inthe vehicle body acceleration α does not have a predetermined magnituderelationship with respect to the first threshold value. For instance,the failure diagnosis unit 158 determines that the acceleration sensor134 is normal if the variance (A2−A1 or A2/A1) in the average value ofthe vehicle body acceleration α is equal to or greater than the firstthreshold value, and determines that the acceleration sensor 134 isfaulty if the variance (A2−A1) or (A2/A1) is smaller than the firstthreshold value.

The failure diagnosis unit 158 determines that the rotational anglesensor 130 is normal if the variance in the average value of the crankangular velocities ω has a predetermined magnitude relationship withrespect to a predetermined second threshold value, and determines thatthe rotational angle sensor 130 is faulty if the variance in the averagevalue of the crank angular velocities ω does not have the predeterminedmagnitude relationship with respect to the predetermined secondthreshold value. For example, the second threshold value is “1”, and ifthe variance (Ω1−Ω2 or Ω1/Ω2) in the average value of the crank angularvelocity ω is smaller than 1, the rotational angle sensor 130 isdetermined to be normal. Conversely, if the variance (Ω1−Ω2 or Ω1/Ω2) isequal to or greater than “1”, the rotational angle sensor 130 isdetermined to be faulty.

The failure diagnosis unit 158 determines that the current sensor 136 isnormal if the variance in the motor current value i has a predeterminedmagnitude relationship with respect to a third threshold value, anddetermines that the current sensor 136 is faulty if the variance in themotor current value i does not have the predetermined magnituderelationship with respect to the third threshold value. For instance,with the third threshold value selected as “1”, the failure diagnosisunit 158 determines that the current sensor 136 is normal if thevariance (I2−I1 or I2/I1) in the average value of the motor currentvalue i is smaller than “1”, and determines that the current sensor 136is faulty if the variance (I2−I1) or (I2/I1) is equal to or greater than“1”.

In this way, the failure diagnosis unit 158 can individually detectfailures of the rotational angle sensor 130, the acceleration sensor134, and the current sensor 136. The failure determination of thesensors 130, 134, 136 described above by the failure diagnosis unit 158may be limited to the case where the true state of the determinationcondition has persisted for a predetermined time period.

The motor drive control unit 164 selects the first pedal forceestimation calculation unit 152, the second pedal force estimationcalculation unit 154, or the third pedal force estimation calculationunit 156 that corresponds to the rotational angle sensor 130, theacceleration sensor 134, or the current sensor 136 that is notdetermined to be faulty by the failure diagnosis unit 158, and forwardsa control command for the drive torque to the motor drive circuit 170 sothat the electric motor 58 is operated with an electric power (currentor voltage) that corresponds to the pedal force estimated by theselected pedal force estimation calculation unit.

In a particular embodiment of the present invention, when theacceleration sensor 134 is determined to be normal by the failurediagnosis unit 158, the motor drive control unit 164 controls the driveof the electric motor 58 by forwarding a control command correspondingto the pedal force estimated by the first pedal force estimationcalculation unit 152.

When the acceleration sensor 134 is determined to be faulty by thefailure diagnosis unit 158, the motor drive control unit 164 controlsthe drive of the electric motor 58 by forwarding a control commandcorresponding to the pedal force estimated by the second pedal forceestimation calculation unit 154 to the motor drive circuit 170, insteadof the pedal force estimated by the first pedal force estimationcalculation unit 152.

When the rotational angle sensor 130 is determined to be faulty by thefailure diagnosis unit 158, the motor drive control unit 164 controlsthe drive of the electric motor 58 by forwarding a control commandcorresponding to the pedal force estimated by the third pedal forceestimation calculation unit 156 to the motor drive circuit 170, insteadof the pedal force estimated by the second pedal force estimationcalculation unit 154.

When the failure diagnosis unit 158 determines that the current sensor136 is faulty, in addition to the acceleration sensor 134 and therotational angle sensor 130, the motor drive control unit 164 controlsthe drive of the electric motor 58 to be stopped.

Thus, unless all of the rotational angle sensor 130, the accelerationsensor 134, and the current sensor 136 should fail, or in other words,if any one of the rotational angle sensor 130, the acceleration sensor134, and the current sensor 136 is normal, the power assist operation bythe electric motor 58 is maintained. As a result, the possibility thatthe power assist operation is terminated due to the failure of thesensors that detect the state quantities used for estimating the pedalforce is reduced so that the possibility of imposing a physical burdento the user owing to the loss of the power assist operation can bereduced.

The crank rotational direction determination unit 160 determines if thecrankshaft 24 is rotating in the normal direction or in the reversedirection from the change in the crank angle θc detected by therotational angle sensor 130. When the crank rotational directiondetermination unit 160 determines that the crankshaft 24 is rotating inthe reverse direction, the motor drive control unit 164 controls thedrive of the electric motor 58 to stop. As a result, unnecessary powerassist is not provided when the crankshaft 24 is rotating in the reversedirection.

The pedal force detection unit 162 determines the presence/absence ofpedal force being applied to the pedal 30, or if the pedal 30 is beingpedaled according to the presence/absence of changes in the rotationalangle θc of the crankshaft 24 detected by the rotational angle sensor130. The motor drive control unit 164 controls to stop the drive of theelectric motor 58 when the pedal force detection unit 162 determinesthat there is no pedal force. As a result, unnecessary power assist isnot provided when there is no pedal force.

The motor drive circuit 170 quantitatively controls the electric powersupplied from the battery 120 to the electric motor 58 according to thecontrol command from the motor drive control unit 164. As a result, theelectric motor 58 is enabled to assist pedaling with a drive torquedetermined from the estimated value of the pedal force.

The motor drive control unit 164 further controls to increase ordecrease the rotational output of the electric motor 58 according to theinclination of the bicycle 10 in the lateral direction and the fore andaft direction detected by the inclination angle sensor 138. As a result,when the bicycle 10 is tilted in the lateral direction during corneringor the like, the pedaling assist is weakened, and when the bicycle 10 istilted in the fore and aft direction on an uphill road or the like, thepedaling assist is strengthened.

As a result, appropriate pedaling assist is provided in various runningconditions without excess or deficiency.

The motor drive control unit 164 further performs a correction controlfor reducing the rotational output of the electric motor 58 in responseto a decrease in the voltage of the battery 120 detected by the voltagesensor 140. As a result, excessive discharging of the battery 120 can beavoided so that the service life of the battery 120 can be extended. Inaddition, the power consumption of the battery 120 is reduced so thatthe assist continuation distance (time) with a single charge of thebattery 120 can be extended.

Next, the control routine of the control unit 150 according to thepresent embodiment will be described in the following with reference tothe flowchart shown in FIG. 9 .

This control routine is initiated when the power of the electric powerassist device 50 is turned on, and a standby state process is performedfirst of all (step ST10). The standby state process includes a processwhereby the various sensors 130, 132, 134, 136, 138, 140 are poweredinto an active state, and the electric motor 58 is put into a stoppedstate.

Next, it is determined if the power supply of the electric power assistdevice 50 has transitioned from on to off (step ST11). When the power ischanged from on to off (step ST11: Yes), a power-off process isperformed (step ST12). The power-off process includes a process wherebypower supply to the sensors 130, 132, 134, 136, 138, 140 is terminated.

When the power supply has not transitioned to off (step ST11: No), it isdetermined if the crankshaft 24 is rotating in the normal direction fromthe signal provided by the rotational angle sensor 130 (step ST13). Ifthe crankshaft 24 is not rotating in the normal direction (step ST12:No), or, in other words, if the pedal 30 is not being pedaled, theprocess flow returns to the standby state process (step ST10), and theelectric motor 58 is maintained in the stopped state without providingpower assist.

When the crankshaft 24 is rotating in the normal direction (step ST12:Yes), items such as parameters and correction values associated with theslope in the road surface in the estimation of the pedal force are set(step ST14). The setting of the items associated with the slope in theroad surface is performed according to the inclination angle of thebicycle 10 in the fore and aft direction, or the state of the slope inthe road surface which can be detected from the signal from theinclination angle sensor 138. For example, when the bicycle 10 istraveling on a downhill road, the estimated value of the pedal force isset to decrease or become zero regardless of the acceleration in thefore and aft direction of the vehicle body detected by the accelerationsensor 134. When the bicycle 10 is traveling on an uphill road, theestimated value of the pedal force based on the fore and aftacceleration of the vehicle body is set to be greater as compared to thecase where the bicycle 10 is traveling on a flat road surface. Further,when the bicycle 10 is cornering, the estimated value of the pedal forcebased on the acceleration in the lateral direction of the vehicle bodyis set to be smaller as compared to the case where the bicycle 10 istraveling on a flat road surface.

Next are calculated the average value A1 of the vehicle bodyacceleration α over the crank angle range θ1 and the average value A2 ofthe vehicle body acceleration α over the crank angle range θ2 detectedby the acceleration sensor 134, the average value Ω1 of the crankangular velocity ω over the crank angle range θ1 and the average valueΩ2 of the crank angular velocity ω over the crank angle range θ2calculated from the crank angle θc detected by the rotational anglesensor 130, and the average value I1 of the motor current i over thecrank angle range θ1 and the average value I2 of the motor current iover the crank angle range θ2 detected by the current sensor 136 (stepST15).

Next, it is determined if the average value A2−average value A1 of thevehicle body acceleration α is equal to or greater than a predeterminedfirst threshold value S1 (step ST16).

If the average value A2−average value A1 is equal to or greater than thefirst threshold value S1 (step ST16: Yes), the pedal force of thebicycle 10 is estimated from the average value A2−average value A1 (stepST17). The motor drive command value is calculated from the estimatedvalue of the pedal force (step ST18), and the signal of thecorresponding motor drive command value is outputted to the motor drivecircuit 170 (step ST19).

As a result, the electric motor 58 is driven according to the pedalforce of the bicycle 10 estimated from the average value A2−averagevalue A1 of the vehicle body acceleration α, and electric power assistis provided according to the pedal force of the bicycle 10.

If the average value A2−average value A1 is smaller than the firstthreshold value S1 (step ST16: No), since it can be assumed that theacceleration sensor 134 is faulty, it is determined if the average valueΩ1/average value Ω2 of the crank angular velocity ω is smaller than “1”(second threshold value Ω) which is set in advance (step ST20). Thedetermination in step ST20 may also be performed by comparing the crankangular velocity ω1 at a crank angle θc=0 degrees with the crank angularvelocity ω2 at a crank angle θc=90 degrees.

If the average value Ω1/average value Ω2 is smaller than “1” (step ST20:No), then it is determined if the average value Ω1/average value Ω2 issmaller than a predetermined threshold value Sω which is greater than“1” (Step ST21).

If the average value Ω1/average value Ω2 is smaller than the thresholdvalue Sω (step ST21: Yes), the pedal force of the bicycle 10 isestimated from the average value Ω2/average value Ω1 (step ST22). Themotor drive command value is calculated from the estimated pedal force(step ST18), and the signal of the corresponding motor drive commandvalue is outputted to the motor drive circuit 170 (step ST19).

As a result, when the acceleration sensor 134 is faulty, the signal ofthe motor drive command value estimated from the average valueA2/average value A1 of the crank angular velocity ω is outputted to themotor drive circuit 170 before the program flow returns to step ST13.

If the average value Ω1/average value Ω2 is equal to or greater than thethreshold value Sω (step ST21: No), the motor drive command value is setto a predetermined small fixed value (step ST23), and the signal of thecorresponding motor drive command value is outputted to the motor drivecircuit 170 (step ST19). As a result, the electric motor 58 is drivenwith a low torque, and a weak electric assist is provided.

If the average value Ω1/average value Ω2 is equal to or greater than “1”(step ST20: Yes), since it can be assumed that the rotational anglesensor 130 is faulty, it is determined if the average value I2/averagevalue I1 of the motor current value i is smaller than “1” (thirdthreshold value S3) (step ST24).

If the average value I2/average value I1 is smaller than “1” (step ST24:Yes), it is determined if the average value I2/I1 is smaller than apredetermined threshold value Iω greater than “1”. (Step ST25).

If the average value I2/I1 is smaller than the threshold value Iω (stepST25: Yes), a calculation is performed to estimate the pedal force ofthe bicycle 10 from the average value I1/I2 (step ST26), and the motordrive command value is calculated from the estimated value of the pedalforce (step ST18). The signal of the thus obtained motor drive commandvalue is outputted to the motor drive circuit 170 (step ST19).

As a result, when the rotational angle sensor 130 fails in addition tothe acceleration sensor 134, the electric motor 58 is driven accordingto the pedal force of the bicycle 10 estimated from the average valueI2/I1 of the motor current value i. As a result, electric power assistis provided according to the pedal force of the bicycle 10.

If the average value I2/I1 is equal to or greater than the thresholdvalue Iω (step ST25: No), the motor drive command value is set to apredetermined small fixed value (step ST23), and the signal of thecorresponding motor drive command value is outputted to the motor drivecircuit 170 (step ST19). As a result, the electric motor 58 is drivenwith a low torque, and a weak electric power assist is provided.

If the average value I2/I1 is equal to or greater than “1” (step ST24:No), it can be assumed that the current sensor 136 is faulty, inaddition to the acceleration sensor 134 and the rotational angle sensor130, so that a failure display is made by lighting a warning lamp or thelike, and the electric motor 58 is stopped (step ST27) before theprocess flow returns to step ST10.

As a result, when all of the acceleration sensor 134, the rotationalangle sensor 130, and the current sensor 136 are faulty, the electricmotor 58 is stopped.

A control unit 150 according to another embodiment of the presentinvention will be described in the following.

The first pedal force estimation calculation unit 152, the second pedalforce estimation calculation unit 154, the third pedal force estimationcalculation unit 156, the crank rotational direction determination unit160, and the pedal force detection unit 162 of the present embodimentare substantially the same as those of the previous embodiment describedabove.

The failure diagnosis unit 158 of the present embodiment determines thatall of the rotational angle sensor 130, the acceleration sensor 134 andthe current sensor 136 are normal in case where the variance (Ω2−Ω1 orΩ2/Ω1) between the average values Ω1 and Ω2 of the crank angularvelocity ω is equal to or greater than a predetermined fifth thresholdvalue and the variance between the values A1 and A2 (A2−A1 or A2/A1) isequal to or greater than the predetermined fourth threshold value, ifthe variance between the average motor current values I1 and I2 (I1−I2or I1/I2) is equal to or greater than the predetermined sixth thresholdvalue and the variance (Ω2−Ω1 or Ω2/Ω1) between the average values Ω1and Ω2 of the crank angular velocity ω is equal to or greater than thepredetermined fifth threshold value.

In this case, the motor drive control unit 164 outputs to the motordrive circuit 170 a control command based on the pedal force estimatedby the first pedal force estimation calculation unit 152 from thevehicle body acceleration α, the pedal force estimated by the secondpedal force estimation calculation unit 154 from the crank angularvelocity ω, or the pedal force estimated by the third pedal forceestimation calculation unit 156 from the motor current value i.

The failure diagnosis unit 158 determines that the acceleration sensor134 is faulty in case where the variance (Ω2−Ω1 or Ω2/Ω1) between theaverage values Ω1 and Ω2 of the crank angular velocity ω is equal to orgreater than the predetermined fifth threshold value and the variance(A2−A1 or A2/A1) between the average values A1 and A2 of the vehiclebody acceleration α is smaller than the predetermined fourth thresholdvalue, if the variance (I1−I2 or I1/I2) between the average values I1and I2 of the motor current values i is smaller than the sixth thresholdvalue and the variance (A2−A1 or A2/A1) between the average values A1and A2 of the vehicle body acceleration α is smaller than thepredetermined fourth threshold value.

In this case, the motor drive control unit 164 outputs to the motordrive circuit 170 a control command based on the pedal force estimatedby the second pedal force estimation calculation unit 154 from the crankangular velocity ω, or the pedal force estimated by the third pedalforce estimation calculation unit 156 from the motor current value i.

The failure diagnosis unit 158 determines that the rotational anglesensor 130 is faulty in case where the variance (Ω2−Ω1 or Ω2/Ω1) betweenthe average value Ω1 and Ω2 of the crank angular velocity ω is equal toor greater than the predetermined fifth threshold value and the variance(A2−A1 or A2/A1) between the average values A1 A2 of the vehicle bodyacceleration α is smaller than the predetermined fourth threshold value,if the variance (I1−I2 or I1/I2) between the average values I1 and I2 ofthe motor current values i is smaller than the sixth threshold value andthe variance (A2−A1 or A2/A1) between the average values A1 and A2 ofthe vehicle body acceleration α is smaller than the fourth thresholdvalue.

In this case, the motor drive control unit 164 outputs to the motordrive circuit 170 a control command based on the pedal force estimatedby the first pedal force estimation calculation unit 152 from thevehicle body acceleration α, or the pedal force estimated by the thirdpedal force estimation calculation unit 156 from the motor current valuei.

The failure diagnosis unit 158 determines that the current sensor 136 isfaulty in case where the variance (Ω2−Ω1 or Ω2/Ω1) between the averagevalues Ω1 and Ω2 of the crank angular velocity ω is equal to or greaterthan the predetermined fifth threshold value and the variance (A2−A1 orA2/A1) between the average values A1 and A2 of the vehicle bodyacceleration α is equal to or greater than the predetermined fourththreshold value, if the variance (I1−I2 or I1/I2) between the averagevalues I1 and I2 of the motor current values i is equal to or greaterthan the sixth threshold value and the variance (Ω2−Ω1 or Ω2/Ω1) betweenthe average value Ω1 and Ω2 of the crank angular velocity ω is smallerthan the fifth threshold value.

In this case, the motor drive control unit 164 outputs to the motordrive circuit 170 a control command to the motor drive circuit 170 basedon the pedal force estimated by the first pedal force estimationcalculation unit 152 from the vehicle body acceleration α, or the pedalforce estimated by the second pedal force estimation calculation unit154 from the crank angular velocity ω.

Further, the failure diagnosis unit 158 determines that the currentsensor 136 is also faulty in case where the acceleration sensor 134 isdetermined to be faulty, the variance (I1−I2 or I1/I2) between theaverage values I1 and I2 of the motor current values i is equal to orgreater than the sixth threshold value and the variance (Ω2−Ω1 or Ω2/Ω1)between the average values Ω1 and Ω2 of the crank angular velocity ω isequal to or greater than the fifth threshold value, if the variance(I1−I2 or I1/I2) between the average value I1 and I2 of the motorcurrent value i is equal to or greater than the sixth threshold value.

In this case, the motor drive control unit 164 outputs to the motordrive circuit 170 a control command based on the pedal force estimatedby the second pedal force estimation calculation unit 154 from the crankangular velocity ω.

Further, the failure diagnosis unit 158 determines that the rotationalangle sensor 130 is also faulty in case where the acceleration sensor134 is determined to be faulty if the variance (I1−I2 or I1/I2) betweenthe average values I1 and 12 of the motor current values i is equal toor greater than the sixth threshold value and the variance (Ω2−Ω1 orΩ2/Ω1) between the average values Ω1 and Ω2 of the crank angularvelocity ω is smaller than the fifth threshold value.

In this case, the motor drive control unit 164 outputs to the motordrive circuit 170 a control command based on the pedal force estimatedby the third pedal force estimation calculation unit 156 from the motorcurrent value i.

Further, when the failure diagnosis unit 158 determines that the currentsensor 136 is also faulty in case where the acceleration sensor 134 isdetermined to be faulty, the variance (Ω2−Ω1 or Ω2/Ω1) between theaverage values Ω1 and Ω2 of the crank angular velocity ω is smaller thanthe fifth threshold value and the variance (I1−I2 or I1/I2) between theaverage values I1 and I2 of the motor current values i is equal to orgreater than the sixth threshold value if the ratio (I2/I1) of theaverage values of the motor current value i is greater than “1”.

In this case, the motor drive control unit 164 outputs to the motordrive circuit 170 a control command for stopping the drive of theelectric motor 58.

Further, the failure diagnosis unit 158 determines that the currentsensor 136 is also faulty in the event where the rotational angle sensor130 is determined to be faulty, the variance (I1−I2 or I1/I2) betweenthe average values I1 and 12 of the motor current values i is equal toor greater than the sixth threshold value and the variance (A2−A1 orA2/A1) between the average values A1 and A2 of the vehicle bodyacceleration α is equal to or greater than the fourth threshold value ifthe variance (A2−A1 or A2/A1) between the average values A1 and A2 ofthe vehicle body acceleration α is equal to or greater than the fourththreshold value S4 and the variance (I1−I2 or I1/I2) between the averagevalues I1 and I2 of the motor current value i is smaller than the sixththreshold value S6.

In this case, the motor drive control unit 164 outputs to the motordrive circuit 170 a control command based on the pedal force estimatedby the first pedal force estimation calculation unit 152 from thevehicle body acceleration α.

Further, the failure diagnosis unit 158 determines that the accelerationsensor 134 is also faulty in case where the rotational angle sensor 130is determined to be faulty if the variance (I1−I2 or I1/I2) between theaverage values I1 and 12 of the motor current values i is equal to orgreater than the sixth threshold value, and the variance (A2−A1 orA2/A1) between the average values A1 and A2 of the vehicle bodyacceleration α is smaller than the fourth threshold value.

In this case, the motor drive control unit 164 outputs to the motordrive circuit 170 a control command based on the pedal force estimatedby the third pedal force estimation calculation unit 156 from the motorcurrent value i.

Further, the failure diagnosis unit 158 determines that the currentsensor 136 is also faulty in the event where the rotational angle sensor130 is determined to be faulty, the variance (I1−I2 or I1/I2) betweenthe average values I1 and 12 of the motor current values i is equal toor greater than the sixth threshold value, and the variance (A2−A1 orA2/A1) between the average values A1 and A2 of the vehicle bodyacceleration α is smaller than the fourth threshold value, if the ratio(I2/I1) of the average values of the motor current values i is largerthan “1”.

In this case, the motor drive control unit 164 outputs to the motordrive circuit 170 a control command for stopping the drive of theelectric motor 58.

Further, the failure diagnosis unit 158 determines that the rotationalangle sensor 130 is also faulty in the event where the current sensor136 is determined to be faulty, the variance (Ω2−Ω1 or Ω2/Ω1) betweenthe average values Ω1 and Ω2 of the crank angular velocity ω is equal toor greater than the fifth threshold value, and the variance (A2−A1 orA2/A1) between the average values A1 and A2 of the vehicle bodyacceleration α is equal to or greater than the fourth threshold value,if the variance (Ω2−Ω1 or Ω2/Ω1) between the average values Ω1 and Ω2 ofthe crank angular velocity ω is smaller than the fifth threshold value,and the variance (A2−A1 or A2/A1) of the average values A1 and A2 of thevehicle body acceleration α is equal to or greater than the fourththreshold value.

In this case, the motor drive control unit 164 outputs to the motordrive circuit 170 a control command based on the pedal force estimatedby the first pedal force estimation calculation unit 152 from thevehicle body acceleration α.

Further, the failure diagnosis unit 158 determines that the accelerationsensor 134 is also faulty in the event where the current sensor 136 isdetermined to be faulty, if the variance (Ω2−Ω1 or Ω2/Ω1) between theaverage values Ω1 and Ω2 of the crank angular velocity ω is equal to orgreater than the fifth threshold value, and the variance (A2−A1 orA2/A1) between the average values A1 and A2 of the vehicle bodyacceleration α is smaller than the fourth threshold value.

In this case, the motor drive control unit 164 outputs to the motordrive circuit 170 a control command based on the pedal force estimatedby the second pedal force estimation calculation unit 154 from the crankangular velocity ω.

Further, when the failure diagnosis unit 158 determines that therotational angle sensor 130 is also faulty in the event where thecurrent sensor 136 is determined to be faulty, the variance (Ω2−Ω1 orΩ2/Ω1) between the average values Ω1 and Ω2 of the crank angularvelocity ω is equal to or greater than the fifth threshold value, andthe variance (A2-A1 or A2/A1) between the average values A1 and A2 ofthe vehicle body acceleration α is smaller than the fourth thresholdvalue, if the ratio of the average values of the crank angular velocityω (Ω1/Ω2) is greater than “1”.

In this case, the motor drive control unit 164 outputs to the motordrive circuit 17 a control command for stopping the drive of theelectric motor 58.

Owing to this control process, in this embodiment also, unless all ofthe rotational angle sensor 130, the acceleration sensor 134, and thecurrent sensor 136 are faulty, or as long as at least one of therotational angle sensor 130, the acceleration sensor 134, and thecurrent sensor 136 is normal, the power assist operation by the electricmotor 58 is maintained. As a result, the possibility that the powerassist operation is stopped due to the failure of the sensors thatdetect the state quantities used for estimating the pedal force isreduced, and the possibility of imposing a physical burden of pedalingto the driver due to the ceasing of the power assist operation isreduced.

Next, the control routine of the control unit 150 of the presentembodiment will be described in the following with reference to theflowchart shown in FIG. 10 .

This control routine is initiated when the power of the electric powerassist device 50 is turned on, and a standby state processing isperformed first of all (step ST30). The standby state process includes aprocess of bringing the sensors 130, 132, 134, 136, 138, 140 into anactive state by feeding power and a process of placing the electricmotor 58 in a stopped state.

Next, it is determined if the state of power supply of the electricpower assist device 50 has changed from on to off (step ST31). When thestate of power supply is changed from on to off (step ST31: Yes), apower-off process is performed (step ST32). The power-off processincludes a process of stopping power supply to the sensors 130, 132,134, 136, 138, 140.

If the power supply has not changed to off (step ST31: No), it isdetermined if the crankshaft 24 is rotating in the normal direction fromthe signal supplied by the rotational angle sensor 130 (step ST33). Ifthe crankshaft 24 is not rotating in the normal direction (step ST33:No), or if the pedal 30 is not being pedaled, the process flow returnsto the standby state process (step ST30), and the electric motor 58 ismaintained in the stopped state without providing power assist.

If the crankshaft 24 is rotating in the normal direction (step ST33:Yes), items such as parameters and correction values associated with asloping road surface in the estimation of the pedal force are set (stepST34). The setting of the items associated with a sloping road surfaceis performed according to the inclination angle of the bicycle 10 in thefore and aft direction, or the state of the sloping road surface whichcan be known from the signal from the inclination angle sensor 138. Forexample, when the bicycle 10 is traveling on a downhill road, theestimated value of the pedal force is set to decrease or become zeroregardless of the acceleration in the fore and aft direction of thevehicle body detected by the acceleration sensor 134. When the bicycle10 is traveling an uphill slope, the estimated value of the pedal forcebased on the acceleration in the fore and aft direction of the vehiclebody is set to be larger than that when traveling on a flat road.Further, when the bicycle 10 is cornering, the estimated value of thepedal force based on the acceleration in the lateral direction of thevehicle body is set to be smaller than that when traveling on a flatroad.

Next, the average values A1 and A2 of the vehicle body acceleration αdetected by the acceleration sensor 134 over the crank angle range θ1and the crank angle range θ2, respectively, the average values Ω1 and Ω2of the crank angular velocity ω calculated from the crank angle θcdetected by the rotational angle sensor 130 over the crank angle rangeθ1 and the crank angle range θ2, respectively, and the average values I1and I2 of the motor current value i detected by the current sensor 136over the crank angle range θ1 and the rotational angle range θ2,respectively, are calculated (step ST35).

Next, it is determined if the average value A2−average value A1 of thevehicle body acceleration α is smaller than the predetermined fourththreshold value S4 when the average value Ω2/average value Ω1 of thecrank angular velocity ω is equal to the predetermined fifth thresholdvalue S5. (Step ST36).

When the average value Ω2/average value Ω1 of the crank angular velocityω is smaller than the predetermined fifth threshold value S5, and theaverage value A2−average value A1 of the vehicle body acceleration α isequal to or greater than the fourth threshold value S4 (step ST36: No),it is determined if the average value Ω2/average value Ω1 of the crankangular velocity ω is smaller than the fifth threshold value S5 when theaverage value I1/I2 of the motor current value i is equal to or greaterthan the predetermined sixth threshold value S6 (Step ST37).

If the average value Ω2/average value Ω1 of the crank angular velocity ωis equal to or greater than the fifth threshold value S5 when theaverage value I1/I2 of the motor current value i is equal to or greaterthan the predetermined sixth threshold value S6 (Step ST37: No), normalprocess is executed (step ST38), and a motor drive command value basedon the pedal force estimated by the normal process is outputted (stepST39) before the process flow returns to step ST33.

If the average value Ω2/average value Ω1 of the crank angular velocity ωis equal to or greater than the fifth threshold value S5 when theaverage value I1/I2 of the motor current value i is equal to or greaterthan the predetermined sixth threshold value S6 (Step ST37: Yes), sincethe current sensor 136 can be assumed as having failed, a current sensorfailure process is executed (step ST40), and the motor drive commandvalue based on the pedal force estimated from the current sensor failureprocess is outputted (Step ST39) before the process flow returns to stepST33.

If the average value A2−average value A1 of the vehicle bodyacceleration α is smaller than the fourth threshold value S4 (step ST36:Yes) when the average value Ω2/average value Ω1 of the crank angularvelocity ω is the fifth threshold value S5, it is determined if theaverage value A2−average value A1 of the vehicle body acceleration α issmaller than the fourth threshold value S4 when the average value I1/I2of the motor current value i is smaller than the sixth threshold valueS6 (Step ST41).

If the average value A2−average value A1 of the vehicle bodyacceleration α is smaller than the fourth threshold value S4 when theaverage value I1/I2 of the motor current value i is smaller than thesixth threshold value S6 and (step ST41: Yes), since the rotationalangle sensor 130 can be assumed as having failed, the rotational anglesensor failure process is executed (step ST42), and the motor drivecommand value based on the pedal force estimated from the rotationalangle sensor failure process is outputted (step ST39) before the processflow returns to step ST33.

If the average value A2−average value A1 of the vehicle bodyacceleration α is equal to or greater than the fourth threshold value S4when the average value I1/I2 of the motor current value i is smallerthan the sixth threshold value S6 (step ST41: No), since theacceleration sensor 134 can be assumed as having failed, theacceleration sensor failure process is executed (step ST42), and themotor drive command value based on the estimated pedal force isoutputted (step ST39) before the process flow returns to step ST33.

Next, the normal process routine will be described in the following withreference to FIG. 11 .

First of all, it is determined if the average value A2−average value A1of the vehicle body acceleration α is equal to or greater than athreshold value Sα (step ST50).

If the average value A2−average value A1 of the vehicle bodyacceleration α is equal to or greater than the threshold value Sa (stepST50: Yes), the calculation for estimating the pedal force of thebicycle 10 is executed based on the average value A2−average value A1 ofthe vehicle body acceleration α (Step ST51), and the motor drive commandvalue is calculated based on the estimated value of the pedal force(step ST52) before the normal process routine is concluded.

As a result, the electric motor 58 is driven according to the pedalforce of the bicycle 10 estimated from the vehicle body acceleration α,and electric power assist is provided.

If the average value A2−average value A1 of the vehicle bodyacceleration α is smaller than the threshold value Sa (step ST50: No),it is then determined if the ratio Ω2/Ω1 of the average values of thecrank angular velocity ω is equal to or greater than the predeterminedthreshold value Sω (step ST53).

If the ratio Ω2/Ω1 of the average values of the crank angular velocity ωis equal to or greater than the threshold value Sω (step ST53: Yes), thepedal force of the bicycle 10 is estimated by calculation from theaverage value Ω2/average value Ω1 of the crank angular velocity ω (stepST54), and based on the estimated value of the pedal force, the motordrive command value is calculated (step ST52) before the normal processroutine is concluded.

As a result, the electric motor 58 is driven according to the pedalforce of the bicycle 10 estimated from the crank angular velocity ω, andelectric power assist is provided.

If the average value Ω2/Ω1 of the crank angular velocity ω is smallerthan the threshold value Sω (step ST53: No), then it is determined ifthe average value I2/average value I1 of the motor current value i issmaller than a predetermined threshold value Si (step ST55).

If the average value I2/average value I1 of the motor current value i issmaller than the threshold value Si (step ST55: Yes), calculation isperformed to estimate the pedal force of the bicycle 10 from the averagevalue I1/average value I2 of the motor current value i (step ST56), andthe motor drive command value is calculated from the estimated value ofthe pedal force (step ST52) before the normal process routine isconcluded.

As a result, the electric motor 58 is driven according to the pedalforce of the bicycle 10 estimated from the motor current value i, andelectric power assist is provided.

If the average value I2/average value I1 of the motor current value i isequal to or greater than the threshold value Sω (step ST55: No), themotor drive command value is set to a predetermined small fixed value(step ST57), and the normal process routine is concluded. As a result,the electric motor 58 is driven with a low torque, and a weak electricpower assist is provided.

Next, a current sensor failure process routine will be described in thefollowing with reference to FIG. 12 .

First of all, a warning is displayed to the effect that the currentsensor 136 is faulty (step ST69).

Next, it is determined if the average value A2−average value A1 of thevehicle body acceleration α is equal to or greater than the fourththreshold value S4 when the average value Ω2/average value Ω1 of thecrank angular velocity ω is equal to or greater than the fifth thresholdvalue S5 (Step ST70).

If the average value A2−average value A1 of the vehicle bodyacceleration α is equal to or greater than the fourth threshold value S4when the average value Ω2/average value Ω1 of the crank angular velocityω is equal to or greater than the fifth threshold value S5 (step ST70:Yes), since the acceleration sensor 134 can be assumed to be normal, itis determined if the average value Ω2/average value Ω1 of the crankangular velocity ω is equal to or greater than the fifth threshold valueS5 when the average value A2−average value A1 of the vehicle bodyacceleration α is equal to or greater than the fourth threshold value S4(step ST71).

If the average value Ω2/average value Ω1 of the crank angular velocity ωis equal to or greater than the fourth threshold value S4 when theaverage value A2−average value A1 of the vehicle body acceleration α isequal to or greater than the fifth threshold value S5 (step ST71: Yes),since the rotational angle sensor 130 can be also assumed to be normal,it is then determined if the average value A2−average value A1 of thevehicle body acceleration α is equal to or greater than the thresholdvalue Sa (step ST72).

If the average value A2−average value A1 of the vehicle bodyacceleration α is equal to or greater than the threshold value Sa (stepST72: Yes), the calculation for estimating the pedal force of thebicycle 10 is performed based on the average value A2−average value A1of the vehicle body acceleration α (Step ST73), and the motor drivecommand value is calculated from the estimated value of the pedal force(step ST74) before the current sensor failure process routine isconcluded.

As a result, the electric motor 58 is driven according to the pedalforce of the bicycle 10 estimated from the vehicle body acceleration α,and the electric power assist is provided.

If the average value Ω2/average value Ω1 of the crank angular velocity ωis smaller than the fifth threshold value S5 when the average valueA2−average value A1 of the vehicle body acceleration α is equal to orgreater than the fourth threshold value S4 (step ST71: No), since therotational angle sensor 130 can be also be assumed as being faulty, theprocess flow skips step ST72 and proceeds to step ST73.

If the average value A2−average value A1 of the vehicle bodyacceleration α is smaller than the threshold value Sa (step ST72: No),it is then determined if the average value Ω1/average value Ω2 of thecrank angular velocity ω is smaller than the predetermined thresholdvalue Sω (step ST75).

If the average value Ω1/average value Ω2 of the crank angular velocity ωis smaller than the threshold value Sω (step ST72: Yes), the pedal forceof the bicycle 10 is estimated from the average value Ω2/average valueΩ1 of the crank angular velocity ω (step ST76), and the motor drivecommand value is calculated from the estimated value of the pedal force(step ST74) before the current sensor failure process routine isconcluded.

As a result, the electric motor 58 is driven according to the pedalforce of the bicycle 10 estimated from the crank angular velocity ω, andelectric power assist is provided.

If the average value Ω1/average value Ω2 of the crank angular velocity ωis equal to or greater than the threshold value Sω (step ST75: No), themotor drive command value is set to a predetermined small fixed value(step ST77), and the current sensor failure process routine isconcluded. As a result, the electric motor 58 is driven with a lowtorque, and a weak electric assist is provided.

If the average value Ω2/average value Ω1 of the crank angular velocity ωis smaller than the fourth threshold value S4 when the average valueA2−average value A1 of the vehicle body acceleration α is equal to orgreater than the fifth threshold value S5 (step ST70: No), since theacceleration sensor 134 can also be assumed as being faulty, it isdetermined if the average value Ω1/average value Ω2 of the crank angularvelocity ω is equal to or greater than “1” (step ST80).

If the average value Ω1/average value Ω2 of the crank angular velocity ωis smaller than “1” (step ST80: No), the process flow proceeds to stepST75 described above, and step ST76 or step ST77, and step ST74 isexecuted. Thereby, electric power assist according to the pedal force ofthe bicycle 10 estimated from the crank angular velocity ω or weakelectric power assist is provided.

If the average value Ω2/average value Ω1 of the crank angular velocity ωis equal to or greater than “1” (step ST80: Yes), since the rotationalangle sensor 130 can also be determined to assumed to be faulty, afailure is displayed by lighting a warning lamp or the like, and theelectric motor 58 is stopped (step ST81) before the process flow returnsto step ST30.

Thus, when all of the acceleration sensor 134, the rotational anglesensor 130, and the current sensor 136 are faulty, the electric motor 58is stopped.

Next, the rotational angle sensor failure process routine will bedescribed in the following with reference to FIG. 13 .

First of all, a warning is displayed to the effect that the rotationalangle sensor 130 is faulty (step ST89).

Next, it is determined if the average value A2−average value A1 of thevehicle body acceleration α is equal to or greater than the fourththreshold value S4 when the average value I1/average value I2 of themotor current value i is equal to or greater than the sixth thresholdvalue S6 (Step ST90).

If the average value A2−average value A1 of the vehicle bodyacceleration α is equal to or greater the fourth threshold value S4 whenthe average value/average value I2 of the motor current value i is equalto or greater than the sixth threshold value S6 (step ST90: Yes), sincethe acceleration sensor 134 can also be assumed as being normal, it isdetermined if the average value I1/average value I2 of the motor currentvalue i is equal to the sixth threshold value S6 when the average valueA2−average value A1 of the vehicle body acceleration α is equal to orgreater than the fourth threshold value S4 (Step ST91).

If the average value I1/average value I2 of the motor current value i isequal to or greater the sixth threshold value S6 when the average valueA2−average value A1 of the vehicle body acceleration α is equal to orgreater the fourth threshold value S4 (step ST91: Yes), since thecurrent sensor 136 can also be assumed as being normal, it is determinedif the average value A2−average value A1 of the vehicle bodyacceleration α is equal to or greater than the threshold value Sa (stepST92).

If the average value A2−average value A1 is equal to or greater than thethreshold value Sa (step ST92: Yes), the pedal force of the bicycle 10is estimated from the average value A2−average value A1 of the vehiclebody acceleration α (step ST93), and the motor drive command value iscalculated from the estimated value of the pedal force (step ST94)before the current sensor failure process routine is concluded.

As a result, the electric motor 58 is driven according to the pedalforce of the bicycle 10 estimated from the vehicle body acceleration α,and the electric power assist is provided.

If the average value A2−average value A1 of the vehicle bodyacceleration α is equal to or greater than the fourth threshold value S4when the average value I1/average value I2 of the motor current value iis smaller than the sixth threshold value S6 (step ST91: No), since thecurrent sensor 136 can also be assumed as being faulty, the processskips step ST92 and proceeds to step ST93.

If the average value A2−average value A1 of the vehicle bodyacceleration α is smaller than the threshold value Sa (step ST92: No),it is then determined if the average value I2/average value I1 of themotor current value i smaller than the predetermined threshold value Si(step ST95).

If the average value I2/average value I1 of the motor current value i issmaller than the threshold value Si (step ST96: Yes), the pedal force ofthe bicycle 10 is estimated from the average value I1/average value I2of the motor current value I by calculation (step ST96), and a motordrive command value is calculated from the estimated value of the pedalforce (step ST94) before the current sensor failure process routine isconcluded.

As a result, the electric motor 58 is driven according to the pedalforce of the bicycle 10 estimated from the motor current value i, andelectric power assist is provided.

If the average value I2/average value I1 of the motor current value i isequal to or greater than the threshold value Si (step ST96: No), themotor drive command value is set to a predetermined small fixed value(step ST97) before the current sensor failure process routine isconcluded. As a result, the electric motor 58 is driven with a lowtorque, and a weak electric assist is provided.

If the average value A2−average value A1 of the vehicle bodyacceleration α is smaller than the fourth threshold value S4 when theaverage value I1/average value I2 of the motor current value i is equalto or greater than the sixth threshold value S6 (step ST90: No), sincethe acceleration sensor 134 can be assumed as being faulty, it is thendetermined if the average value I2/average value I1 of the motor currentvalue i is equal to or greater than “1” (step ST100).

If the average value I1/average value I2 of the motor current value i issmaller than 1 (step ST100: No), the process flow proceeds to step ST95described above, and step ST96 or step ST94 is executed. As a result,electric assist according to the pedal depression force of the bicycle10 estimated from the motor current value i or weak electric assist isprovided.

If the average value I1/average value I2 of the motor current value i is1 or greater (step ST100: Yes), since the current sensor 136 can also beassumed as being faulty, a failure is displayed by lighting a warninglamp or the like and the electric motor 58 is stopped (step ST101)before the process returns to step ST30.

Thus, when all of the acceleration sensor 134, the rotational anglesensor 130, and the current sensor 136 are faulty, the electric motor 58is stopped.

Next, the acceleration sensor failure process routine will be describedin the following with reference to FIG. 14 .

First, a warning is displayed to the effect that the acceleration sensor134 is faulty (step ST109).

Next, it is determined if the average value Ω2/average value Ω1 of thecrank angular velocity ω is equal to or greater than the fifth thresholdvalue S5 when the average value I1/average value I2 of the motor currentvalue i is equal to or greater than the sixth threshold value S6. (StepST110).

If the average value Ω2/average value Ω1 of the crank angular velocity ωis equal to or greater than the fifth threshold value S5 when theaverage value/average value I2 of the motor current value i is equal toor greater than the sixth threshold value S6 (step ST110: Yes), sincethe rotational angle sensor 130 can be assumed as being normal, next, itis determined if the average value I1/average value I2 of the motorcurrent value i is equal to or greater than the sixth threshold value isS6 when the average value Ω2/average value Ω1 of the crank angularvelocity ω is equal to or greater than the fifth threshold value S5(step ST111).

If the average value I1/average value I2 of the motor current value i isequal to or greater than the sixth threshold value S6 when the averagevalue Ω2/average value Ω1 of the crank angular velocity ω is equal to orgreater than the fifth threshold value S5 (step ST111: Yes), since thecurrent sensor 136 can also be assumed as being normal, next, it isdetermined if the average value Ω2/average value Ω1 of the crank angularvelocity ω is equal to or greater than the threshold value Sω (stepST112).

If the average value Ω2/average value Ω1 of the crank angular velocity ωis equal to or greater than the threshold value Sω (step ST112: Yes),the pedal force of the bicycle 10 is estimated from the average valueΩ2/average value Ω1 of the crank angular velocity ω by calculation (stepST113), and the motor drive command value is calculated from theestimated value of the pedal force (step ST114) before the accelerationsensor failure process routine is concluded.

As a result, the electric motor 58 is driven according to the pedalforce of the bicycle 10 estimated from the crank angular velocity ω, andelectric power assist is provided.

If the average value Ω2/average value Ω1 of the crank angular velocity ωis smaller than the threshold value Sω (step ST112: No), it isdetermined if the average value I2/average value I1 of the motor currentvalue i is smaller than a predetermined threshold value Si (step ST115).

If the average value I2/average value I1 of the motor current value i issmaller than the threshold value Si (step ST116: Yes), the pedal forceof the bicycle 10 is estimated from the average value I1/average valueI2 of the motor current value I by calculation (step ST116), and themotor drive command value is calculated from the estimated value of thepedal force (step ST114) before the acceleration sensor failure processroutine is concluded.

As a result, the electric motor 58 is driven according to the pedaldepression force of the bicycle 10 estimated based on the motor currentvalue i, and electric assist is performed.

If the average value I1/average value I2 of the motor current value i issmaller than the sixth threshold value S6 when the average valueΩ2/average value Ω1 of the crank angular velocity ω is equal to orgreater than the fifth threshold value S5 (step ST111: No), since thecurrent sensor 136 can also be assumed as being faulty, the process flowskips step ST112 and proceeds to step ST113.

If the average value I2/average value I1 of the motor current value i isequal to or greater than a threshold value Si (step ST115: No), themotor drive command value is set to a predetermined small fixed value(step ST117), and the current sensor failure process routine isconcluded. As a result, the electric motor 58 is driven with a lowtorque, and a weak electric power assist is provided.

If the average value Ω2/average value Ω1 of the crank angular velocity ωis smaller than the fifth threshold value S5 when the average valueI1/average value I2 of the motor current value i is equal to or greaterthan the sixth threshold value S6 (step ST110: No), since the rotationalangle sensor 130 can also be assumed to be faulty, next, it isdetermined if the average value I2/average value I1 of the motor currentvalue i is equal to or greater than “1” (step ST120).

If the average value I1/average value I2 of the motor current value i issmaller than “1” (step ST120: No), the process flow proceeds to stepST115 described above, and step ST76 or step ST77, and step ST74 areexecuted. As a result, electric assist based on the pedal force of thebicycle 10 estimated from the motor current value i or a weak electricpower assist is provided.

If the average value I1/average value I2 of the motor current value i isequal to or greater than “1” (step ST118: No), since the current sensor136 can be assumed as being faulty, a failure is displayed by lighting awarning lamp or the like and the electric motor 58 is stopped (stepST201) before the process flow returns to step ST30.

As a result, when all of the acceleration sensor 134, the rotationalangle sensor 130, and the current sensor 136 are faulty, the electricmotor 58 is stopped.

Owing to these processes, the possibility of stopping the power assistoperation due to a failure of the sensors is reduced, and thepossibility of increasing the physical burden of pedaling on the driverin the electrically assisted bicycle can be reduced.

Although the present invention has been described above with respect topreferred embodiments thereof, the present invention is not limited tosuch embodiments, and can be appropriately modified without departingfrom the spirit of the present invention. The crank angle ranges θ1 andθ2 are not limited to the angle ranges shown in FIG. 5 . For example, inthe normal rotational direction, it may be selected such that the crankangle range θ1=330 degrees to 30 degrees, and the crank angle rangeθ2=30 to 90 degrees. The vehicle body acceleration α, crank angularvelocity ω, and motor current value i that are used for failuredetermination may be given not only by the average values over the crankangle ranges θ1 and θ2, but may also be given as values of the crankangle θc at single points within the crank angle ranges θ1 and θ2.

In addition, not all of the components shown in the above-describedembodiments are indispensable, but they can be appropriately selectedand omitted without deviating from the scope of the present invention.

LIST OF REFERENCE NUMERALS

 10: bicycle  12: seat tube  14: down tube  16: chain stay  18: framestructure  20: bearing tube  24: crankshaft  24A: spline shaft portion 24B: screw hole  26: crank arm  26A: spline hole  26B: screw hole  27:crank arm mounting screw  28: crank arm  30: pedal  32: drive sprocket 50: electric power assist device  52: housing  54: ring portion  56:extension portion  58: electric motor  60: central opening  62:cylindrical portion  64: rotary output member  66: boss portion  70:coupling mechanism  72: coupling main member  73: inclined edge part 74: clamp member  75: bolt  76: bolt  78: screw member  80: bolt  81:through hole  90: support mechanism  92: mounting member  94: fasteningband  96: rectangular frame part  98: support base member 100:rectangular plate-shaped part 102: depending piece 103: through hole104: support member 106: fixed bush 108: female screw 109: male screw110: movable bush 112: flange part 114: fastening bolt 120: battery 130:rotational angle sensor (rotational angle detection device) 132: pulsesensor 134: acceleration sensor (acceleration detection device) 136:current sensor (current detection device) 138: inclination angle sensor140: voltage sensor 150: control unit 152: first pedal force estimationcalculation unit 154: second pedal force estimation calculation unit156: third pedal force estimation calculation unit 158: failurediagnosis unit 160: crank rotational direction determination unit 162:pedal force presence/absence determination unit 164: motor drive controlunit 166: failure display 170: motor drive circuit

1. An electric power assist device configured to be fitted to a bicycle,comprising; an electric motor connected to a crankshaft configured to bedriven by a pedal force applied to a pedal of the bicycle via a crankarm or to the crank arm in a torque transmission relationship; a first,a second and a third state quantity detecting unit configured toindividually detect a first, a second and a third state quantity whichare mutually distinct for estimating the pedal force of the bicycle; anda control unit configured to control an operation of the electric motorbased on outputs of the first, the second and the third state quantitydetecting units, wherein the control unit includes: a first pedal forceestimating computation unit configured to estimate the pedal force ofthe bicycle according to a variance between values of the first statequantity at two mutually different crank angle positions; a second pedalforce estimating computation unit configured to estimate the pedal forceof the bicycle according to a variance between values of the secondstate quantity at two mutually different crank angle positions; a thirdpedal force estimating computation unit configured to estimate the pedalforce of the bicycle according to a variance between values of the thirdstate quantity at two mutually different crank angle positions; a motordrive control unit configured to control a drive of the electric motoraccording to a selected one of the pedal forces estimated by the first,the second and the third state quantity detecting units; and a failurediagnosis unit configured to diagnose failures of the first, the secondand the third state quantity detecting units by evaluating the variancesin the values of first, the second and the third state quantities. 2.The electric power assist device according to claim 1, wherein the motordrive control unit is configured to control the drive of the electricmotor according to the pedal force estimated by one of the first pedalforce estimating computation unit, the second pedal force estimatingcomputation unit, and the third pedal force estimating computation unitcorresponding to one of the first to the third state quantity detectingunits that is diagnosed to be not faulty by the failure diagnosis unit.3. The electric power assist device according to claim 1, wherein one ofthe two mutually different crank angle positions includes a top deadcenter of the pedal, and another of the two mutually different crankangle positions includes a crank angle position 90 degrees sway from thetop dead center of the pedal.
 4. The electric power assist deviceaccording to claim 1, wherein the first pedal force estimationcalculation unit is configured to estimate the pedal force according toa variance between average values of the first state quantity averagedover two rotational angle ranges containing the two mutually differentcrank angle positions, respectively, the second pedal force estimationcalculation unit is configured to estimate the pedal force according toa variance between average values of the second state quantity averagedover two rotational angle ranges containing the two mutually differentcrank angle positions, respectively, and the third pedal forceestimation calculation unit is configured to estimate the pedal forceaccording to a variance between average values of the third statequantity averaged over two rotational angle ranges containing the twomutually different crank angle positions, respectively.
 5. The electricpower assist device according to claim 1, wherein the first to thirdstate quantity detecting units are selected from an acceleration sensorfor detecting a fore and aft acceleration of the bicycle, a rotationalangle sensor for detecting a crank angle and a crank angular velocity ofthe crankshaft, and a current sensor for detecting a motor current valueof the electric motor.
 6. The electric power assist device according toclaim 1, wherein the failure diagnosis unit is configured to determinethe failures of the first to third state quantity detecting units bycomparing the variances between the values of the first to third statequantities with corresponding first to third threshold values,respectively.
 7. The electric power assist device according to claim 6,wherein the failure diagnosis unit is configured to diagnose the firststate quantity detecting unit to be normal when the variance in regardto the first state quantity is in a prescribed magnitude relationship tothe first threshold value, and the first state quantity detecting unitto be faulty when the variance in regard to the first state quantity isnot in the prescribed magnitude relationship to the first thresholdvalue; the failure diagnosis unit is configured to diagnose the secondstate quantity detecting unit to be normal when the variance in regardto the second state quantity is in a prescribed magnitude relationshipto the second threshold value, and the second state quantity detectingunit to be faulty when the variance in regard to the second statequantity is not in the prescribed magnitude relationship to the secondthreshold value; and the failure diagnosis unit is configured todiagnose the third state quantity detecting unit to be normal when thevariance in regard to the third state quantity is in a prescribedmagnitude relationship to the third threshold value, and the third statequantity detecting unit to be faulty when the variance in regard to thethird state quantity is not in the prescribed magnitude relationship tothe third threshold value.
 8. The electric power assist device accordingto claim 6, wherein the motor drive control unit is configured tocontrol the drive of the electric motor according to the pedal forceestimated by the first pedal force estimating computation unit when thefirst pedal force estimating computation unit is determined to be normalby the failure diagnosis unit; to control the drive of the electricmotor according to the pedal force estimated by the second pedal forceestimating computation unit instead of the first pedal force estimatingcomputation unit when the first pedal force estimating computation unitis determined to be faulty by the failure diagnosis unit; to control thedrive of the electric motor according to the pedal force estimated bythe third pedal force estimating computation unit instead of the secondpedal force estimating computation unit when the second pedal forceestimating computation unit is determined to be faulty by the failurediagnosis unit; and to terminate the drive of the electric motor whenthe third pedal force estimating computation unit is determined to befaulty by the failure diagnosis unit.
 9. The electric power assistdevice according to claim 1, wherein the failure diagnosis unit isconfigured to determine the failures of the first to third statequantity detecting units by comparing the variances in regards to thefirst to third state quantities with one another.
 10. The electric powerassist device according to claim 1, wherein the first state quantitydetecting unit includes an acceleration sensor for measuring a fore andaft acceleration of the bicycle, the second state quantity detectingunit includes a rotational angle sensor for detecting a crank angle anda crank angular velocity of the crankshaft, and the third state quantitydetecting unit includes a current sensor for detecting a motor currentvalue of the electric motor.
 11. The electric power assist deviceaccording to claim 1, wherein the failure diagnosis unit is configuredto diagnose all of the acceleration sensor, the rotational angle sensor,and the current sensor to be normal in case where the variance in thevehicle body acceleration between the two mutually different crankshaftangles is equal to or greater than a fourth threshold value when thevariance in the crankshaft angular velocity between the two mutuallydifferent crankshaft angles is equal to or greater than a fifththreshold value, if the variance in the crank angular velocity betweenthe two mutually different crankshaft angles is equal to or greater thana fifth threshold value when the variance in the motor current betweenthe two mutually different crankshaft angles is equal to or greater thana sixth threshold value; to diagnose that the acceleration sensor to befaulty in case where the variance in the vehicle body accelerationbetween the two mutually different crankshaft angles is smaller than thefourth threshold value when the variance in the crankshaft angularvelocity between the two mutually different crankshaft angles is equalto or greater than the fifth threshold value if the variance in thevehicle body acceleration between the two mutually different crankshaftangles is equal to or greater than the fourth threshold value when thevariance in the motor current between the two mutually differentcrankshaft angles is smaller than the sixth threshold value; to diagnosethat the rotational angle sensor to be faulty in case where the variancein the vehicle body acceleration between the two mutually differentcrankshaft angles is smaller than the fourth threshold value when thevariance in the crankshaft angular velocity between the two mutuallydifferent crankshaft angles is equal to or greater than the fifththreshold value if the variance in the vehicle body acceleration betweenthe two mutually different crankshaft angles is smaller than the fourththreshold value when the variance in the motor current between the twomutually different crankshaft angles is equal to or greater than thesixth threshold value; and to diagnose that the motor current sensor tobe faulty in case where the variance in the vehicle body accelerationbetween the two mutually different crankshaft angles is equal to orgreater than the fourth threshold value when the variance in thecrankshaft angular velocity between the two mutually differentcrankshaft angles is equal to or greater than the fifth threshold valueif the variance in the crankshaft angular velocity between the twomutually different crankshaft angles is smaller than the fifth thresholdvalue when the variance in the motor current between the two mutuallydifferent crankshaft angles is equal to or greater than the sixththreshold value.
 12. The electric power assist device according to claim11, wherein the failure diagnosis unit diagnoses that the current sensoris also faulty in case where the acceleration sensor is diagnosed to befaulty, and the variance in the crank angular velocity is equal to orgreater than the fifth threshold value when the variance in the motorcurrent value is equal to or greater than the sixth threshold value ifthe variance in the motor current value is smaller than the sixththreshold value when the variance in the crank angular velocity is equalto or greater than the fifth threshold value; that the rotational anglesensor is also faulty if the acceleration sensor is diagnosed to befaulty, and the variance in the crank angular velocity is smaller thanthe fifth threshold value when the variance in the motor current valueis equal to or greater than the sixth threshold value; that the currentsensor is also faulty in case where the rotational angle sensor isdiagnosed to be faulty, and the variance in the vehicle bodyacceleration is equal to or greater than the fourth threshold value whenthe variance in the motor current values is equal to or greater than thesixth threshold value if the variance of the motor current value issmaller than the sixth threshold value when the variance in the vehiclebody acceleration is equal to or greater than the fourth thresholdvalue; that the acceleration sensor is faulty if the rotational anglesensor is diagnosed to be faulty, and the variance in the vehicle bodyacceleration is smaller than the fourth threshold value when thevariance in the motor current value is equal to or greater than thesixth threshold value; that the rotational angle sensor is also faultyin case where the current sensor is diagnosed to be faulty, and thevehicle body acceleration is equal to or greater than the fourththreshold value when the variance in the crank angular velocity is equalto or greater than the fifth threshold value if the crank angularvelocity is smaller than the fifth threshold value when the variance inthe vehicle body acceleration is equal to or greater than the fourththreshold value; and that the acceleration sensor is also faulty if thecurrent sensor is diagnosed to be faulty, and the vehicle bodyacceleration is smaller than the fourth threshold value when the crankangular velocity is equal to or greater than the fifth threshold value.13. A bicycle fitted with the electric power assist device according toclaim 1.